A conventional prior art hydraulic damper or shock absorber comprises a cylinder which is adapted at one end for attachment to the sprung or unsprung mass of a vehicle. A piston is slidably disposed within the cylinder with the piston separating the interior of the cylinder into two fluid chambers. A piston rod is connected to the piston and extends out of one end of the cylinder where it is adapted for attachment to the other of the sprung or unsprung mass of the vehicle. A first valving system is incorporated within the piston as a safety hydraulic relief valve during the shock absorber's extension stroke of the piston with respect to the cylinder and a second valving system is incorporated within the piston for allowing fluid replenishment above the piston during the shock absorber's compression stroke of the piston with respect to the cylinder.
Various types of adjustment mechanisms have been developed to generate variable damping forces in relation to the speed and/or the amplitude of the displacement of the sprung mass in relation to the unsprung mass. These adjustment mechanisms have mainly been developed to provide a relatively small or low damping characteristic during the normal steady state running of the vehicle and a relatively large or high damping characteristic during vehicle maneuvers requiring extended suspension movements. The normal steady state running of the vehicle is accompanied by small or fine vibrations of the unsprung mass of the vehicle and thus the need for a soft ride or low damping characteristic of the suspension system to isolate the sprung mass from these small vibrations. During a turning or braking maneuver, as an example, the sprung mass of the vehicle will attempt to undergo a relatively slow and/or large movement or vibration which then requires a firm ride or high damping characteristic of the suspension system to support the sprung mass and provide stable handling characteristics to the vehicle. These adjustable mechanisms for the damping rates of a shock absorber offer the advantage of a smooth steady state ride by isolating the high frequency/small amplitude excitations of the unsprung mass while still providing the necessary damping or firm ride for the suspension system during vehicle maneuvers causing low frequency/large excitations of the sprung mass.
The continued development of shock absorbers includes the development of adjustment systems which provide the vehicle designer with a continuously variable system which can be specifically tailored to a vehicle to provide a specified amount of damping in relation to various monitored conditions of the vehicle and its suspension system.